VoltDB Internals

You are here

VoltDB’s new command logging feature reduces the window of data loss during a cluster wide failure from single digit minutes (the window between snapshots) to zero. Command logging can be tuned to give you the same amazing latency and throughput you get from VoltDB, even on a single 7.2k SATA disk. Our unique approach to log based durability exploits the determinism and replication inherent in VoltDB’s architecture to avoid the overhead and latency of ARIES style logging.

How We Log

A command log is kept at every node and contains partially ordered stored procedure invocations.

Many VoltDB applications, such as gaming leader boards and real-time analytics, use multi-partition procedures to compute consistent global aggregates (and other interesting statistics). It’s challenging to efficiently process distributed reads operations, especially for performance sensitive applications. Based on feedback from our users, we in VoltDB engineering have been enhancing the VoltDB SQL planner over the last few releases to improve this capability.

Executing global aggregates efficiently requires calculating sub-results at each partition replica and combining the sub-results at a

When learning about VoltDB for the first time, people often ask how VoltDB executes transactions in a distributed environment. So, here’s how…

Let’s say a developer, Dan, is working on a new website. He’s decided to use VoltDB as part of his data management layer. One of Dan’s users requests a dynamically generated page and the code that generates that page sends a request to Dan’s VoltDB cluster. The excitement begins.

Dan’s code asks the VoltDB client library to execute his procedure named “GetUserProfile” and provides the user’s handle, “dbNerd”, as a parameter.

We, at VoltDB, are excited to tell you about the command logging feature that we’ve been working on this summer. We’ve built this feature because our customers asked for it, and they’ve given us some great feedback on how it should work. Here’s a heads up to get you thinking about how you can make use of this new functionality.

So what’s command logging and why are we so excited about it? First, let me remind you of VoltDB’s snapshot functionality. A database snapshot is exactly what it sounds like — a point-in-time copy of the database contents written to disk.

VoltDB is a relational store that uses SQL for its query language and stored procedures for its transactional unit of work. Clients invoke stored procedures to access the database. Stored procedures access data using parametrized SQL statements and can manipulate intermediate results in Java. Each stored procedure invocation is a transaction. A procedure’s data manipulations are atomic and isolated from other concurrently executing procedures.

Here’s a simple example, excerpted from the Voter sample application shipped with the VoltDB distribution kit.

First and foremost, VoltDB is focused on specific workloads. Most existing RDBMSs are designed to be general purpose, one-size-fits-all systems. Recently, there have been a lot of new databases introduced that achieve better performance by specializing in areas like analytics, graphs or streaming data. Few of these specialized systems focus OLTP, and when they do, it’s often more about tuning, rather then a rethink. VoltDB was designed to be the most scalable transaction processing system out there, often making compromises unsuitable for other workloads.